As the frequency of operation of radar antennas increases, the spacing between the radiating elements that make up the aperture becomes smaller. For example, the spacing may be less than 1.0 cm (0.400″) center-to-center at 16 GHz (Ku band). In addition, effective phased array radars can have 10,000 or more radiating elements. The radiating elements in these millimeter radar assemblies have critical alignment requirements. They require isolation between adjacent radiating elements and excellent grounding. In addition, the radiating elements in millimeter radar assemblies require thermal management due to their high power generation in small effective areas.
Previous processes formed the mechanical attachment between adjacent radiating elements in a phased array aperture with epoxy joints and machined features in soft-substrates such as “Duroid®”. Materials such as polytetrafluoroethylene (PTFE) and “Duroid®” (PTFE/glass or PTFE/ceramic composites) exhibit poor dimensional stability, cold flow characteristics, and deformation under cutting stresses. Unlike metals, features machined in these materials cannot be relied upon to provide the positional alignment required in a high/wide band phased array aperture. Therefore to achieve element-to-element alignment and orientation, radiating elements were assembled using complicated tooling that required tedious fabrication procedures.
For example, element-to-element alignment and orientation of individual radiating elements on individual substrates are often performed using a “rake” tool and a joe block. The rake is used to establish a predetermined spacing between cells in the array, and the individual substrates are then positioned around the joe block to establish the correct orientation and location of the substrates. The array is built up by adding individual radiating elements. In the case of stripline circuit elements assembled in this manner, plated through-holes (vias) were used for isolation between adjacent radiating elements. This type of assembly can also have spurious grounds due to uneven or decaying epoxy joints.
Another previous process used screws to fasten radiating elements to a substrate. However, because the size between the antenna elements of millimeter antennas is so small, a screwed-in approach will not work because even the smallest screws are too large for use in a millimeter antenna array.
An improved array structure and method of making millimeter antenna array is desired.